The present invention relates to a method for separating selected materials in a gas chromatograph, wherein the gas mixture is introduced into a separation column of the gas chromatograph and the separation column is heated inside a chamber of the gas chromatograph to a preset temperature. The invention also provides a gas chromatograph for practicing the method. The gas chromatograph comprises an oven with a heat-resistant and insulating jacket and a closeable chamber, the chamber includes a capillary separation column which is connected to an injector and to a detector, and a heating device.
Gas chromatographs are used in measurement procedures, in particular procedures relating to the environment, for separating and analyzing the various constituent materials in gas mixtures.
For this purpose, a respective gaseous sample is introduced into a gas chromatographic separation column of a gas chromatograph together with a carrier gas and heated inside the gas chromatograph from ambient temperature to a temperature of about 300.degree. C.
The materials evaporate in accordance with their boiling point, are transported by the carrier gas and interact with the gas chromatographic phase which is coated on the inside of the column. The individual compounds thus experience different propagation times inside the column.
This allows the separation of complex organic compounds.
The gas chromatographs consist primarily of a thermally insulated oven with an oven door and a capillary separation column located inside the oven and wound in the form of a circular coil. The separation column is connected to an injector for receiving the gas sample as well as to a detector, for example to a mass spectrometer. The detector and the mass spectrometer, respectively, are provided with a computerized evaluation and display system.
The oven further includes a heating device and a fan coupled to the heating device. A gas chromatograph of this type is known, for example, from U.S. Pat. No. 4,286,456.
The gas chromatograph is highly accurate, so that the experimental results obtained with the method are very conclusive.
Disadvantageously, however, ovens with a large internal volume have to be used, although the long separation column with a length of up to 60 m is not always required. Since the entire oven with its large internal volume and its large mass has to be heated together with the gas, an unnecessarily large amount of energy has to be supplied, while the cool-down times are also prolonged.
It is also disadvantageous that, although frequently only a few compounds are of interest, the entire gas mixture has to be separated by gas chromatography in order to prepare the column for the next analysis. Consequently, the oven and the gas mixture have to be heated to the maximum temperature so that the last compound also exits the column.
As a result, an analysis in large gas chromatographs can take up to about 30 minutes, followed by lengthy cool-down times of about 15 minutes.
The measurement cycles are very long due to the long heating and cooling times and cannot be justified if only a few compounds or a single well defined compound, rather than all compounds, have to be analyzed in the gas mixture.
Moreover, the gas chromatograph is not suited for mobile applications due to its massive construction.